The goal of this research program is exposure of genetic mechaisms controlling cellular differentiation in Drosophila. Alpha-Amylase was selected as an indicator of the state of differentiation of a tissue so that factors regulating its synthesis, properties, location and ultimate fate may be analyzed during development and in response to environmental cues. The tissue of major interest is the midgut. A system is being developed to selectively screen for mutations of "regulatory genes" which control the action and/or expression of the structural gene for amylases, Amy, or its products. Genetic analyses utilize variants for electrophoretic mobility, specific activity and heat stability of the Amy gene. A temporal control gene linked to the structural gene is under analysis. This gene controls the tissue-specific expression of Amy in the posterior midgut. The presence of other temporal genes for amylase is being explored. An aim of the program is to identify the level at which these genes operate. Null mutants for Amy are being sought and among them delections of the structural gene(s) which will be used to locate Amy precisely on the cytological map of chromosome 2R. A starch diet induced, specific "puff" in midgut polytene chromosomes from amylase-active regions of the larval posterior midgut is under study; the puff appears to correlate with increased amylase activity in that tissue and is perhaps an indicator of transcriptional activity at the Amy locus(i). Amylase synthesis compared in specific tissues under the control of the temporal gene which has been defined. An attempt will be made to isolate the mRNA for amylase and use it in a cell free in vitro translating system. Molecular characterization of purified amylase isozymes will continue. The ultrastructural morphology of midgut cells will be studies with regard to the expression of the Amy locus(i).